In October 1912, a crowd of 5,000 watched as President William Taft laid the cornerstone of the Huntington Avenue YMCA. The facility would go on to provide education, exercise facilities, and family programs to generations.

Now, the branch is at a crossroads as it embarks on its next century. As it strengthens its ­array of social services and healthy-living programs, the facility is also undergoing a major overhaul and preparing to accommodate a high-rise dormitory that has raised tension in the Fenway neighborhood.

“That Y is a beacon for many people,” Kevin Washington, president and chief executive of the YMCA of Greater Boston, said of the building with the iconic glowing letters perched atop its roof. “Many times it’s not about the building; it’s about what goes on there. That’s why people stay there.”

The Huntington YMCA has provided countless residents of Boston, the first US city to host a Y, with the tools and support to thrive here. The branch, like all Y’s during the first part of the century, first provided educational, spiritual, and sobriety programs to men, often recent immigrants or sailors, and offered a home to those new to the city.

The organization formed a Student Army Training Corps unit during World War I and offered vocational classes in automobile repair and art, architecture, navigation, surveying, and mathematics.

By 1937, the Y opened its doors to women, ­minorities, and all religions and has since continued to expand its services to children and teenagers and society at large.

Services now include summer camps, part-time jobs for teenagers, education on teen dating violence, and breakfasts and lunches for children ­during the summer. Membership is also open to same-sex couples, and the Y provides rest­rooms to accommodate transgender members.

Its physical education and workout programs have evolved from bulking up for the war to focusing on healthy living and diabetes prevention.

The overhaul to its building, however, is the most dramatic change now underway.

Earlier this year, the ­Huntington Y sold its gym building and Hastings wing to Phoenix Property Co., for $21.5 million, allowing the real estate company to begin building a 17-story dormitory for Northeastern University, which traces its own roots to the Y’s Evening Institute for Young Men.

The deal allowed the Y to ­begin the transformation of its aging structure into a more efficient and fully accessible building and to construct a three-story addition with a new gym, pool, and handball courts.

Y officials hope the changes will allow them to offer services to more families while catering to the urban neighborhood. But the changes have stirred tension.

During a long and often contentious city-approval process, some residents and Y members said the organization was offering too much of its space to Northeastern. Though many agreed the building needed an update, some critics of the deal said they fear the sale of portions of the branch could eventually lead to the loss of the ­entire facility.

“The thing that really was not good was the process; that did not make me feel good about being a Huntington Avenue Y member,” said Maureen Flynn, who has been a member most of her life and is a member of the master’s swim program that swam at the ­Huntington Y for 20 years before the pool closed for demolition.

The team has had to find a new place to swim, Flynn said, and its members have dispersed to pools across the ­Boston area. “I think it will be difficult for people to go back there after 2, 2½ years,” she said.

Washington, however, said the deal was a “win-win” situation, pointing out that the organization was renting much of the space to Northeastern and that the deal allowed the Y to ­leverage its extra space to ­improve its facilities.

The Y has no plans to sell the remainder of the building, he said.

For some of the branch’s oldest and longest members, the facility has remained a constant in their lives.

Waldo Fielding, a 91-year-old retired doctor and Brookline resident, has been a YMCA member since he was 6, when his father started taking him to the Worcester branch.

It was there that Fielding became an athlete. He learned to swim and play table tennis and golf. He went on to swim competitively for Dartmouth College and was ranked sixth ­nationally in table tennis.

Even now, Fielding, a World War II veteran, works out at the Oak Square Y in Brighton twice a week with a personal trainer and regularly visits the ­Huntington branch, where he is known by many staff and members who eagerly greet him.

For Fielding, it is not just about the workout.

“The Y offered me something which went along and still goes along with my basic makeup,” Fielding said after walking on a treadmill at the Huntington Y as the sounds of construction tools whirred in the background.

Fielding said he has always known an accepting and inclusive Y and recalls asking black members to join the table tennis club during his youth.

Margaret Cameron, 35, of Dorchester, spent her afternoons at the Huntington branch as a student and still considers herself a “Y kid.” It’s where she learned to try new things, get along with others, and finish work before playing.

“It was such a part of my life it was so integrated into my life. I never thought of it not in my life,” said Cameron, who met her future husband at the Y’s after­school program when she was just 6.

Their 3-year-old daughter took her first swimming class at the Roxbury Y this summer, and Cameron, who volunteers for the Y, plans to enroll her in other activities so her daughter can experience the community she did. “At its heart, it’s the same Y; they open up their arms to you,” she said.